Opiate receptors are also receptors for naturally occurring peptides called endorphins or enkephalines. Experiments in this laboratory are aimed at clarifying the identity and function of these peptides: Methods for measuring anodynin, a novel opiate peptide in blood, are under study since blood level alterations may accompany various physiological or psychological states. A radioreceptor assay for cerebrospinal levels of endorphines has also been developed. The molecular basis of opiate agonist-antagonist activity is being probed with D-Ala2-enkephalin, a novel synthetic opiate peptide which retains high affinity for opiate receptors but resists enzymatic degradation. BIBLIOGRAPHIC REFERENCES: Coyle, J.T. and Pert, C.B.: Ontogenetic development of (3H)naloxone binding in rat brain. Neuropharmacology, 15: 555-560, 1976. Pert, C.B., Snyder, S.H. and Portoguese, P.S.: Correlation of opiate receptor affinity with analgetic effects of merperidine homologues. J. Med. Chem. 19: 1248-1250, 1976.